How can I lower the idle speed? - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

DamnedButDetermined · 02-28-2003, 11:01 AM

My air conditioning is broken, so my engine should be idling at 7-800rpms. Mine on the other hand is idling SMOOTHLY (i only include the word smoothly b/c there are many threads already about irregular idle [going from 400-900-500-1500-stall, and stuff like that]) at 1000rpm. I took off the air intake piping and shot some carb/choke cleaner into the throttle body to clean out the built up gunk hoping that the butterfly valve would make a better seal and lower the revs. That didn't work! (it does look nice and clean though) I then looked at were the throttle cable connects to the throttle body, and there is a tiny adjuster screw with a nut on it, where if you turn it to the right (after loosening the nut of course) the throttle is opened slightly and revs increase. So i turned it to the left but it didn't lower the revs any. I then checked to see if there were any other adjusters or places ( including the throttle cable) that would keep the butterfly valve from closing any more, but there isn't.

So now to my question...
How can i lower the idle speed?

I have reset my computer before and noticed the screw you turn has a sticker around it that says Idle Speed control. But when you reset the ecu you turn it all the way to the clockwise, start the car, then turn it all the way counter clockwise, meaning that it is at the lowest Idle Speed. Is there anything i can do with that adjuster screw that will lower the speed?

I have also heard that there is an Idle Control Valve at the back of the intake manifold. I am 99% sure i have found this control valve but i didn't see any adjustments that i could make. Is there anything i can do with the Idle Control Valve?

I am planning on completely removing the air conditioning in the future, and will be gutting out my water pump and replacing it with an electric one. These two mods will elimitate a lot of resistance on the engine and will in turn make it idle even higher, so i don't want to have an already high idle before i do this. It will sound quite retarded if i am at a stop light and the engine is at 1600 rpms!

Any and all suggestions are appreciated, and please give me alot of them!

thanks,
-DbD-

EDIT: Damn it I always forget to tell you it is a 1990 fastback

N1ceDrgn · 02-28-2003, 12:24 PM

You have checked out a lot of the common areas. One thing to do is swap out the AAC valve, (where the idle adjustment screw is). I believe that's the proper name for it. You can swap that out and then another thing to do check your vacuum lines. There are too many times they are over looked. With the increase in throttle, it's an 'intake' issue. So, trace out and figure out what deals with your intake. Most of the time a vacuum connection, or a sensor on the throttle body are the main villains. Check around and try to listen for any hissing or leaks. If this is something that just came up, then it may or may not have anything to do with the a/c. At the same time, try to keep in mind that when you use the a/c there is a relay/ switch that ups the idle because the a/c pump is drawing a lot of power/ torque from the engine. So, as a default reaction, the computer ups the RPM's because of what the sensors are telling it. That is the other area to check out. Trouble shoot the a/c system and find out what could be wrong there other than the obvious. I'll do some more thinking but that's what I have for you now.

*AceInHole* · 02-28-2003, 02:28 PM

The idle speed adjusting screw is on the side of the intake plenum towards the firewall. You might want to give that a shot.

Is there a bit of slack in the throttle cable? If the cable is too tight it might be pulling the throttle body slightly open... you said you checked that though, but I'm not sure to what extent you tried adjusting it.

DamnedButDetermined · 02-28-2003, 03:00 PM

oh man you guys are fukin awsome! I checked for vacuum leaks...none...removed the a/c relay switch...nothing...adjusted the idle speed screw....VICTORY IS MINE

It went down from a steady 1000rpms to a steady 750rpms. My car sounds so much better and i might actually get more gas mileage out of this gas gussler!

thanks again,
-DbD-

gregsr20 · 03-03-2003, 04:47 PM

also adjust throttle cable

**Phlip** · 03-03-2003, 05:16 PM

There's also a little screw on underneath the throttle butterfly thingies... I had to change my idle and moved that to change it up for me...

DamnedButDetermined · 03-03-2003, 05:26 PM

phlip can you be a little more specific?

do you mean the little screw inside the throttle body? Or somewere around the outside?

RedlineRacer · 03-03-2003, 09:10 PM

I noticed mine idles at around 500 rpms. Should I advance my timing?

**Phlip** · 03-04-2003, 09:28 AM

Quote:

Originally posted by DamnedButDetermined
phlip can you be a little more specific?

do you mean the little screw inside the throttle body? Or somewere around the outside?

It's on the outside... I wish I had a picture. You know where the throttle cable goes? There's a little screw at the bottom of that, it's on the right... You back the nut that's on it out a touch and then move the screw as you need to adjust the idle. Up for more RPMs, down for less... If my Digi cam's battery wasn't dead, I'd go out and take a picture...

Quote:

Originally posted by RedlineRacer
I noticed mine idles at around 500 rpms. Should I advance my timing?

See above, same applies to you, I was having the same problem...

uiuc240 · 03-04-2003, 09:47 AM

that's the ghetto/old-school way to adjust idle. the idea of the IACV is to keep the throttle plate completely closed, and use the solenoid controlled valve to allow air to bypass the throttle plate. if your IACV is not adjusting properly for idle, you need to fix it...not back out the screw on the throttle body. I made that mistake a while back. I learned my lesson.

Eric

02-28-2003, 11:01 AM	#1
DamnedButDetermined Zilvia Addict Join Date: Oct 2002 Location: Jax, Fl Age: 43 Posts: 637 Trader Rating: (1) Feedback Score: 1 reviews	How can I lower the idle speed? My air conditioning is broken, so my engine should be idling at 7-800rpms. Mine on the other hand is idling SMOOTHLY (i only include the word smoothly b/c there are many threads already about irregular idle [going from 400-900-500-1500-stall, and stuff like that]) at 1000rpm. I took off the air intake piping and shot some carb/choke cleaner into the throttle body to clean out the built up gunk hoping that the butterfly valve would make a better seal and lower the revs. That didn't work! (it does look nice and clean though) I then looked at were the throttle cable connects to the throttle body, and there is a tiny adjuster screw with a nut on it, where if you turn it to the right (after loosening the nut of course) the throttle is opened slightly and revs increase. So i turned it to the left but it didn't lower the revs any. I then checked to see if there were any other adjusters or places ( including the throttle cable) that would keep the butterfly valve from closing any more, but there isn't. So now to my question... How can i lower the idle speed? I have reset my computer before and noticed the screw you turn has a sticker around it that says Idle Speed control. But when you reset the ecu you turn it all the way to the clockwise, start the car, then turn it all the way counter clockwise, meaning that it is at the lowest Idle Speed. Is there anything i can do with that adjuster screw that will lower the speed? I have also heard that there is an Idle Control Valve at the back of the intake manifold. I am 99% sure i have found this control valve but i didn't see any adjustments that i could make. Is there anything i can do with the Idle Control Valve? I am planning on completely removing the air conditioning in the future, and will be gutting out my water pump and replacing it with an electric one. These two mods will elimitate a lot of resistance on the engine and will in turn make it idle even higher, so i don't want to have an already high idle before i do this. It will sound quite retarded if i am at a stop light and the engine is at 1600 rpms! Any and all suggestions are appreciated, and please give me alot of them! thanks, -DbD- EDIT: Damn it I always forget to tell you it is a 1990 fastback

02-28-2003, 12:24 PM	#2
N1ceDrgn Zilvia Member Join Date: Nov 2002 Location: SoCal Posts: 259 Trader Rating: (0) Feedback Score: 0 reviews	You have checked out a lot of the common areas. One thing to do is swap out the AAC valve, (where the idle adjustment screw is). I believe that's the proper name for it. You can swap that out and then another thing to do check your vacuum lines. There are too many times they are over looked. With the increase in throttle, it's an 'intake' issue. So, trace out and figure out what deals with your intake. Most of the time a vacuum connection, or a sensor on the throttle body are the main villains. Check around and try to listen for any hissing or leaks. If this is something that just came up, then it may or may not have anything to do with the a/c. At the same time, try to keep in mind that when you use the a/c there is a relay/ switch that ups the idle because the a/c pump is drawing a lot of power/ torque from the engine. So, as a default reaction, the computer ups the RPM's because of what the sensors are telling it. That is the other area to check out. Trouble shoot the a/c system and find out what could be wrong there other than the obvious. I'll do some more thinking but that's what I have for you now. __________________ ..working on something that is slowly getting built up and restored..

02-28-2003, 02:28 PM	#3
AceInHole Autox Technician Join Date: Dec 2001 Location: New Haven, CT Age: 44 Posts: 3,961 Trader Rating: (0) Rides Gallery: AceInHole Feedback Score: 0 reviews	The idle speed adjusting screw is on the side of the intake plenum towards the firewall. You might want to give that a shot. Is there a bit of slack in the throttle cable? If the cable is too tight it might be pulling the throttle body slightly open... you said you checked that though, but I'm not sure to what extent you tried adjusting it. __________________

03-03-2003, 04:47 PM	#5
gregsr20 Zilvia Member Join Date: Jan 2003 Location: SAVANNAH, GA. Age: 42 Posts: 155 Trader Rating: (0) Feedback Score: 0 reviews	also adjust throttle cable __________________ fast cars are dangerous, save lives drive HONDA'S

03-03-2003, 05:16 PM	#6
Phlip Yes, I look like that Join Date: Mar 2002 Location: In my supervillain's lair Posts: 27,980 Trader Rating: (19) Rides Gallery: Phlip Feedback Score: 19 reviews	There's also a little screw on underneath the throttle butterfly thingies... I had to change my idle and moved that to change it up for me... __________________ Weirdo And I write too!

02-28-2003, 03:00 PM	#4
DamnedButDetermined Zilvia Addict Join Date: Oct 2002 Location: Jax, Fl Age: 43 Posts: 637 Trader Rating: (1) Feedback Score: 1 reviews	oh man you guys are fukin awsome! I checked for vacuum leaks...none...removed the a/c relay switch...nothing...adjusted the idle speed screw....VICTORY IS MINE It went down from a steady 1000rpms to a steady 750rpms. My car sounds so much better and i might actually get more gas mileage out of this gas gussler! thanks again, -DbD-

03-03-2003, 05:26 PM	#7
DamnedButDetermined Zilvia Addict Join Date: Oct 2002 Location: Jax, Fl Age: 43 Posts: 637 Trader Rating: (1) Feedback Score: 1 reviews	phlip can you be a little more specific? do you mean the little screw inside the throttle body? Or somewere around the outside?

03-03-2003, 09:10 PM	#8
RedlineRacer Zilvia FREAK! Join Date: Sep 2002 Location: Clemson, South Carolina Age: 40 Posts: 1,054 Trader Rating: (0) Feedback Score: 0 reviews	I noticed mine idles at around 500 rpms. Should I advance my timing?

03-04-2003, 09:47 AM	#10
uiuc240 Nissanaholic! Join Date: Apr 2002 Location: Naperville, IL Age: 46 Posts: 2,093 Trader Rating: (0) Feedback Score: 0 reviews	that's the ghetto/old-school way to adjust idle. the idea of the IACV is to keep the throttle plate completely closed, and use the solenoid controlled valve to allow air to bypass the throttle plate. if your IACV is not adjusting properly for idle, you need to fix it...not back out the screw on the throttle body. I made that mistake a while back. I learned my lesson. Eric __________________ 2002 Mazda Protege5 1989 S13 w/SR20DET (sold)